1) Field of the Invention
The present invention relates to optical switching devices suitably applicable to the case where the path is switched over based on the light wavelength. For example, the present invention relates to optical switching devices employed in optical switching nodes, which conduct the line switching of the light as it is in an optical fiber communication network system built by applying the wavelength multiplexing technique. In particular, the present invention relates to optical switching devices, which separate the light having multiplexed wavelengths based on the wavelength; then, select plural paths separately based on the respective wavelengths, and finally multiplex a plurality of light beams on the same path to output the light therefrom. Further specifically, the present invention relates to an optical switching device including a plurality of integrated devices, which switches over optical paths between a single-port and a plural-port based on the light wavelengths.
Hereinafter, in this specification, a wavelength-selective optical switch as a device for switching over the optical path based on the light wavelengths is defined as below. That is, at least one port at a side is used as the input port, and the ports other than the input port are used as the output ports; and the switch will be referred to as “(number of input ports)×(number of output ports) wavelength-selective optical switch” based on the number of the input ports and the output ports.
2) Description of the Related Art
A conventional M×M wavelength-selective optical switch is constituted of a plurality of independent 1×N wavelength-selective switches. For example, FIG. 21 shows an example of a conventional M×M (M=3) wavelength-selective optical switch. A 3×3 wavelength-selective switch 100 shown in FIG. 21 is constituted of three 1×N (N=2) wavelength-selective optical switches 101–103 and three N×1 wavelength-selective optical switches 104–106.
That is, the 3×3 wavelength-selective optical switch 100 shown in FIG. 21 is provided with three ports 107-1 to 107-3. It is arranged such that the light, which enters the respective ports 107-1 to 107-3, is outputted selectively to a path to which one of the two ports other than the own port is connected in the 1×2 wavelength-selective optical switches 101–103. Also, in each of the ports 107-1-107-3, the 2×1 wavelength-selective optical switches 104–106 selects one of the signals from a 1×2 wavelength-selective switch in the two ports other than the own port and outputs the signal therefrom. For example, it is arranged such that the light, which enters the port 107-1, is output selectively to a path connect with one of the two ports 107-2 and 107-3 other than the input port in the 1×2 wavelength-selective optical switch 101. And, in the port 107-1, the 2×1 wavelength-selective optical switch 104 selects one of the signals from the 1×2 wavelength-selective switches 102 and 103 in the ports 107-2 and 107-3 other than the port 107-1, and output the signal therefrom. Accordingly, in the 3×3 wavelength-selective optical switch 100 shown in FIG. 21, it is impossible to select a path which returns the signal to the port at the sending side of the signal.
FIG. 22 also is a diagram showing a conventional M×M (M=4) wavelength-selective optical switch 110. The 4×4 wavelength-selective switch 110 shown in FIG. 22 is an example, which is constituted of four 1×4 wavelength-selective optical switches 111 to 114 and four 4×1 wavelength-selective optical switches 115 to 118, and is capable of selecting a path, which returns the signal to a port at the sending side of the signal.
In particular, the optical switch 110 is provided with four ports 119-1 to 119-4. And it is arranged such that the light, which enters each of the ports 119-1 to 119-4, is outputted selectively to a path to which any one of the four ports 119-1 to 119-4 including the input port is connected in the 1×4 wavelength-selective optical switches 111 to 114. And, in each of the ports 119-1 to 119-4, the 4×1 wavelength-selective optical switches 115 to 118 select one of the signals from the 1×4 wavelength-selective switches 111 to 114 in the four ports 119-1 to 119-4 including the own ports 119-1 to 119-4.
For example, it is arranged such that the light, which enters the port 119-1, is outputted selectively to a path connected with any one of the ports 119-1 to 119-4 including the own port 119-1 in the 1×4 wavelength-selective optical switch 111. And in the port 119-1, the 4×1 wavelength-selective optical switch 115 selects one of the signals from the 1×4 wavelength-selective switch 111–114 in the ports 119-1 to 119-4 including the own port 119-1, and outputs the signal therefrom. Accordingly, the 4×4 wavelength-selective optical switch 110 shown in FIG. 22 is capable of selecting a path which returns the signal to the output port at the sending side of the signal.
The 1×N wavelength-selective optical switch and the N×1 wavelength-selective optical switch are the devices used in the above-described M×M wavelength-selective optical switches 100, 110 and the like, which switch over the optical path between the single-port and the plural-port based on the light wavelength. In many cases, the M×M wavelength-selective optical switches 100, 110 are generally obtained with the same constitution by using the wavelength-selective optical switches with their input and output ports inversed each other.
The wavelength-selective optical switches in FIGS. 21 and 22 are shown as a single switch. However, actually, the switches are capable of switching over independently based on the WDM (Wavelength Division Multiplexing) light; i.e., based on the wavelength channel of the wavelength multiplexed light.
The following patent document 1 discloses an example of constitution of a wavelength-selective optical switch as a device for switching over the optical path between the single-port and the plural-port based on the light wavelength, which is used in the M×M wavelength-selective switches as described above.
The 1×N (N×1) wavelength-selective optical switch 120 as a device for switching over the optical path between the single-port and the plural-port based on the light wavelength, which is disclosed in the patent document 1 is constituted of, for example, as show in FIG. 23, ports 121 (121-1, 121-2, . . . ) formed of N optical fibers, first lenses 122 (122-1, 122-2, . . . ) disposed corresponding to each of the ports 121, a diffraction grating 123, a second lens 124 and a movable minute mirror 125.
Further, the following patent documents 2 to 4 disclose examples of constitution of the 1×N (N×1) wavelength-selective optical switches.                [Patent document 1] U.S. Pat. No. 6,549,699 Specification        [Patent document 2] U.S. Pat. No. 6,498,872 Specification        [Patent document 3] Published Japanese translation of PCT international publication application No. 2003-515187        [Patent document 4] U.S. Pat. No. 6,204,946 Specification        
A conventional M×M wavelength-selective switch is constituted of a plurality of; i.e., in general, 2M independent wavelength-selective optical switches, which switch over the optical path between the single-port and the plural-port based on the light wavelength (M of the 1×N wavelength-selective optical switches and M of the N×1 wavelength-selective optical switches). To manufacture the conventional M×M wavelength-selective switch, members of 2M times as many as members necessary for a single 1×N (or N×1) wavelength-selective switch are required. And further, the manhours of 2M times as much as the manhours necessary for assembling a single 1×N (or N×1) wavelength-selective switch is required, thereby leading to the relatively large cost necessary for the entire device. In addition to that, there is such problem that, since M of 1×N wavelength-selective optical switches and M of N×1 wavelength-selective optical switches are used, the size of the entire device becomes larger in proportion to the number of the used 1×N (and N×1) wavelength-selective switches.